Cancer is the uncontrolled proliferation of cells in the body. It develops for two main reasons, environmental and genetic. Environmental causes include radiation, chemicals, and viruses, while internal causes include hereditary mutations, other genetic causes, hormonal factors, and immune disorders.1 

Cancer is one of the most important problems that threaten public health all over the world. With the prolongation of life, the incidence of some forms of cancer has also increased.

Tracheal-bronchial lung cancer, prostate, colorectal, bladder, stomach, non-hodgkin's lymphoma, kidney, larynx, thyroid, brain-nervous system cancers in men; Breast, thyroid, colorectal, uterus-corpus, tracheal-bronchial lung, stomach, ovary, non-hodgkin's lymphoma, uterus-cervix, brain-cervical system cancers are among the top 10 most common cancers in women in Turkey.2

For many years, physical activity has been known to reduce the incidence of age-related chronic diseases such as cardiovascular disease, diabetes, hypertension, and metabolic syndrome. Recent studies have shown that exercise is also beneficial in preventing cancer. Booth et al. 3 have shown that the sedentary lifestyle adopted by most people in developed countries is incompatible with human gene structure. It has been scientifically proven that regular exercise significantly reduces the incidence of many cancers, especially breast 4 and colorectal cancer 5. Exercise is also a supportive treatment method used to reduce the side effects and felt complaints of chemotherapy and radiotherapy in cancer patients. Numerous randomized trials have shown that patients who participate in exercise programs have higher levels of physical function during chemotherapy or radiotherapy than control patients and complain less of psychological problems, fatigue, and other treatment-related symptoms.6

Mechanisms of Effect of Exercise on Cancer

One of the most important mechanisms that provide a relationship between exercise and cancer prevention is weight control and reducing fat, especially in the abdomen. Fatty tissue is the primary source of endogenous estrogen and testosterone, and high levels of these hormones are risk factors for breast, endometrial, and pros-taste cancer. In particular, fat deposition in the abdominal region may increase the production of these hormones and increase the risk of breast cancer, endometrial, and prostate cancer. 7,8,9

Moreover, exercise increases insulin sensitivity, reduces IGF-1, and reduces inflammation, which can be protective against breast cancer. It has been shown in various studies that 10,11
 IGF-1 can increase cell division, especially in breast tissue, causing cell proliferation, reducing the death of cancerous cells, and thus acting as a mitogen. Regular exercise lowers the level of IGF 1 in the blood by increasing the level of IGF-binding protein 3 (IGFBP-3) and thus may help reduce the risk of many cancers, especially breast cancer.12 

The protection of exercise against colon cancer has been attributed to the acceleration of the intestinal passage with increased activity and therefore the reduced risk of encountering carcinogens and mucosa. Other possible mechanisms are increased prostaglandin synthesis with physical activity and the consequent cessation of colon cell proliferation, decreased bile acid concentration and decreased circulating insulin and glucose levels. The underlying mechanisms in the protection of exercise against all types of cancer are listed as decreased body fat mass, stimulation of immune mechanisms against the tumor, increased level of antioxidants, and genetic causes.13

In addition, regular exercise can prevent the shortening of the neck by preserving the telomere structure and reducing the risk of cancer.14 However, the level of free radicals produced when one-time very vigorous exercise is performed may exceed the capacity of the antioxidant defense system and cause oxidative stress. Overproduction of radicals can damage DNA by causing base changes in DNA structure, which can trigger cancer formation by causing changes in gene structure. Therefore, short-term moderate exercise is recommended to reduce the risk of cancer. 14

Exercise in Patients Diagnosed with Cancer

Cancer patients are advised to rest frequently and keep their daily activities to a minimum to prevent and reduce fatigue, but physical inactivity leads to muscle destruction and reduced physical strength and endurance.15 Physical activity has beneficial effects on fatigue, quality of life, muscle strength, depression, and functional capacity in cancer patients. Physical exercise programs increase functional capacity and reduce fatigue. 15, 16

The American Sports Medicine Association recommends regular exercise as part of treatment to maintain or improve physical and psychological well-being in patients with cancer.17

Regular exercise improves physical function, aerobic capacity, strength, and flexibility in patients with cancer and helps to maintain and develop body structure (maintains or increases muscle mass). However, it makes the person feel psychologically well, reduces stress, depression, and anxiety, increases bone mineral density, improves complaints such as nausea, pain, difficulty sleeping, and diarrhea, reduces the length of hospital stay, and strengthens the immune system. 

Depending on the increase in physical  capacity and the decrease in complaints felt due to side   effects, the level of fatigue felt by the patient decreases, and thus an increase in the quality of life of the patient occurs.18, 19

American Sports Medicine Association's recommendations for exercise in cancer patients 17

• It is recommended that patients with cancer avoid inactivity, and it is stated that even a little physical activity is better than no physical activity at all.
• Moderate activity or 75 minutes of high-intensity activity or an equivalent combination is recommended for an aerobic activity for at least 150 minutes per week.
• Exercises involving large muscle groups 2 or 3 times a week are recommended for strengthening.
• Stretching to large muscle groups and tendons is recommended on days when other exercises are performed for flexibility.
• It is recommended that the initial exercise intensity and duration be low and gradually increased as the patient's medical condition allows. 
   

It is stated that the above-mentioned exercise goals are generally suitable for cancer patients, but, if necessary, exercise programs can be adapted according to the health status of individuals, the treatments they receive, and the expected disease curve.

In order to recommend specific exercise programs, the patient's comorbid conditions, and exercise contraindications should be carefully evaluated. In addition, the patient's age, gender, cancer type and treatment, and the patient's physical performance status should also be taken into account. 20

When planning exercise, the most common toxicities related to cancer treatment (fracture risk, cardiovascular events with hormone therapies, neuropathy due to chemotherapy, musculoskeletal diseases secondary to treatment, and cardiotoxicity due to treatment) should be kept in mind. Modification of the exercise program is required due to the increased risk of fracture in patients with bone metastases. When prescribing exercise, exercise should be planned according to the person, taking into account the aerobic fitness of the cancer patient before treatment, accompanying diseases, treatment response, and negative effects of treatment.17

The American Society of Clinical Oncology (ASCO) guidelines for adult cancer patients with fatigue recommend two or three strength training sessions (weight lifting) each week in addition to 150 minutes of moderate aerobic exercise (brisk walking, cycling, or swimming).21

The 2012 American Cancer Society (ACS) guideline recommends: Avoiding inactivity, returning to normal daily activity as soon as possible after diagnosis, and aiming for at least 150 minutes/week of exercise, including exercises that require at least 2 days/week of strength.22,23

Objectives of prescribing exercise in patients with cancer

• To regain and improve physical function, aerobic capacity, strength, and flexibility,
• Improving body image and quality of life,
• Development of cardiorespiratory, endocrine, neurological, muscular, cognitive, and psychosocial status,
• Reducing or delaying potential cancer recurrence or secondary primary cancer,
• To develop the ability to physically and psychosocially resist anxiety due to recurrence or secondary primary cancer,
• Reducing, preserving, and protecting from the long-term and late effects of cancer treatment 17

As a result, being physically active throughout life reduces the risk of many cancers, especially colorectal and breast cancer. Regular exercise after cancer diagnosis provides a decrease in complaints, an improvement in treatment-related side effects, an increase in psychological well-being, and an increase in life expectancy through various mechanisms. All cancer patients should be encouraged to engage in regular physical activity throughout their lives.

Assoc. Prof. Dr.Özgür ORTANCIL 
Yeditepe University Koşuyolu Hospital 
Department of Physical Therapy and Rehabilitation